The present invention relates to a device for actuating an element in the power train of a motor vehicle, such as a clutch-actuating device or a transmission-actuating device.
Such devices are known in general in the existing state of the art. For example, DE 195 04 847 may be named as a reference for a device proposed earlier by the assignee of the present invention. Actuating devices of the type described herein are used, e.g., with friction clutches in the power trains of motor vehicles. In friction clutches, the force required for the release (disengagement) of the clutch depends among other factors on the magnitude of the torque being transmitted through the clutch. Thus, different motor vehicles with different engines will require different clutch-release forces. Also, the required speed of actuation may vary. In an actuator that is powered by an electric motor, an upper limit of the actuating force is dictated by the size of the electric motor, which has to fit into the available space. Also, with a larger motor, friction losses would use up a considerable part of the added power.
Nevertheless, actuators for clutches and transmissions need to be matched to the greatest diversity of dimensional requirements. This has the disadvantage that a large number of different actuator designs have to be developed, with each different actuator model being used only in small numbers.
It is therefore the object of the present invention to provide a concept for an actuating device, where a smaller number of different actuator designs can satisfy the requirements of a given number of different vehicle models.
To meet the foregoing objective, the present invention provides an actuating device for an operating element in the power train between the engine and the driven wheels of a motor vehicle. The inventive actuating device is distinguished in that it employs at least two actuators arranged in parallel to actuate the operating element.
In practical applications, the operating element will normally be a clutch or a transmission.
It is of practical advantage if the parallel actuators can be operated simultaneously at least part of the time.
It is likewise of practical advantage if the parallel actuators can be operated sequentially at least part of the time.
In advantageous embodiments of the invention, each of the parallel actuators has its own electric motor. It has practical benefits if the electric current to the motors is turned on during sequentially staggered time intervals.
It is further advantageous if the actuators work together in parallel during part of the time to actuate the clutch or other operating element.
According to a further concept of the invention, it is of practical benefit in an arrangement of two actuators with two electric motors, if the electric current to the second motor is switched on only after the start-up current of the first motor has fallen below a prescribed threshold value.
It is further practical if the start-up current of one or the other or both motors is limited so that the sum of the currents does not exceed a prescribed limit.
The novel features that are considered as characteristic of the invention are set forth in particular in the appended claims. The improved apparatus itself, however, both as to its construction and its mode of operation, together with additional features and advantages thereof, will be best understood upon perusal of the following detailed description of certain presently preferred specific embodiments with reference to the accompanying drawing.